| Insecticides are the key weapons to control insect pests and to reduce the losses of agricultural products. Continuous development of new insecticides with selective properties and specific action is necessary for pest control.Butene-fipronil is a novel phenylpyrazole compound and has lower toxicity to fish than fipronil.It is an excellent insecticide for control of many pest species in Lepidoptera, Hemiptera, Coleoptera and Orthopteran. However, the insecticidal efficiency of butene-fipronil to dipterans remains undetermined.Drosophila melanogaster is easy to care for, breeds quickly, and lays many eggs, it is an excellent model animal to assess the toxicity of butene-fipronil.In the present study, we investigated the toxicity and potential risk of butene-fipronil to Drosophila melanogaster larvae and adults in the laboratory.1. Assessment of toxicity and potential risk of butene-fipronil using Drosophilamelanogaster, in comparison to nine conventional insecticidesThe toxicity of butene-fipronil to Drosophila melanogaster was evaluated, in comparison to nine conventional insecticides. According to the mean LC50 values of the larvae from CS, w1’18 and Oregan strains, butene-fipronil, abamectin, spinosad and chlorpyrifos exhibited high levels of toxicity. Imidacloprid, a-cypermethrin and clothianidin showed middle levels of toxicity. And acephate, methomyl and acetamiprid had low levels of toxicity. To the adults, butene-fipronil, a-cypermethrin, spinosad, and chlorpyrifos were relatively higher toxic, whereas acephate, methomyl, acetamiprid, imidacloprid, clothianidin and abamectin were relatively lower toxic. A comparison of the toxicities between the larvae and the adults revealed that butene-fipronil and abamectin were more toxic to larvae than those to the adults, with the ratios of LC50 values for adults to corresponding LC50 values for larvae of 16 and 45 respectively. In contrast, spinosad, a-cypermethrin, and clothianidin were more toxic to adults. Moreover, the toxic risk of the ten tested insecticides to the adults was estimated using risk quotient values. Chlorpyrifos, a-cypermethrin and spinosad were slightly to moderately toxic to D. melanogaster. In contrast, acephate, methomyl, imidacloprid, acetamiprid, clothianidin, butene-fipronil and abamectin were safe to D. melanogaster. Thus, our results suggested that butene-fipronil is harmful to D. melanogaster larvae, and at the same time, it is relatively safe to the adults.We gave several possible explanations to the result that butene-fipronil and abamectin were more toxic to larvae than those to the adults. Firstly, butene-fipronil may be a slow-acting insecticide, it may not exhibit its maximum toxic effects to the adults within 24 hour. Secondly, larvae and adults may have different detoxification abilities. Thirdly, butene-fipronil may negatively affect larval pupation and adult emergence. We will test the three possibilities in the following researches.2. Evaluation of speed of toxic action of butene-fipronil and seven conventional insecticides in Drosophila melanogaster adults.Continuous development of new insecticides with selective properties and specific action is necessary for pest control. Butene-fipronil is a novel compound obtained via the structural modification of fipronil, and has lower toxicity to fish than fipronil. In the present paper, we compared the toxic feature of butene-fipronil with seven conventional insecticides. We found that butene-fipronil, a-cypermethrin, and spinosad were high toxic, where as acephate, endosulfan, methomyl, imidacloprid, and abamectin were relatively low toxic to D. melanogaster adults. The speed of toxic action of butene-fipronil to Drosophila melanogaster adults was determined using the ratio of LC50 values evaluated 24,48,72 and 96 hours after treatment, in comparison to the seven conventional insecticides, of which imidacloprid and abamectin are slow-acting insecticides, and acephate, endosulfan, methomyl, a-cypermethrin and spinosad are fast-acting insecticides. Our results revealed that all the 5 fast-acting insecticides caused high adult death within 24 or 48 hours after treatment. Further exposure only slightly increased the mortality of D. melanogaster adults. In contrast, the LC50 value in D. melanogaster adults for the 2 slow-acting insecticides was almost linearly decreased with increased exposure period. The ratio of LC50 value for butene-fipronil was 1.00,0.65,0.41 and 0.25 after 24,48,72 and 96 hours of treatment, almost completely mimicked the variation of slow-acting insecticides. Thus, butene-fipronil belongs to slow-acting insecticides. Our results provide more empirical information for butene-fipronil potential application.Moreover, our results indicated the slow-acting characters of butene-fipronil and abamectin may partially contribute to their toxicity difference between the larvae and the adults.3. The detoxification of the larvae and adults of Drosophila melanogaster to butene-fipronilPiperonylbutoxide (PBO), triphenyl phosphate (TPP) and diethylmeleate (DEM) were selected test synergistic effects on butene-fipronil. The co-toxicity indices of butene-fipronil+PBO, butene-fipronil+TPP and butene-fipronil+DEM mixtures were 437.3,335.0 and 210.3 respectively in the second instar larvae, and were 186.6,256.2 and 238.5 respectively in the adults, indicating synergistic effects. Moreover, we found that butene-fipronil increased Cyp28A5 mRNA level in the larvae, enhanced expression of Cyp18A1, Cyp9F2, Cyp304A1, Cyp28A5, and Cyp318A1 in the female adults, and upregulated expression of Cyp303A1 and Cyp28A5 in the male adults. Furthermore, we discovered that butene-fipronil slightly increased Est-7 mRNA level at the second-instar larvae, enhanced the expression of Est-7 at the male adults, and greatly upregulated the expression of Est-7 at the female adults.These data revealed that detoxification by cytochrome P450 monooxygenases, esterases and glutathione-S-transferases was not responsible for the difference in toxicity of butene-fipronil between the larvae and the adults of D. melanogaster.4. The influence of butene-fipronil on the pupation of Drosophila melanogasterThe influence of butene-fipronil, fipronil, abamectin and acephate were evaluated on the pupation of D. melanogaster. When the larvae were dietarily exposed to butene-fipronil, fipronil and abamectin, the rates of non-metamorphosizing larvae increased in a dose-dependent manner. Correlation analysis revealed that the probit rate of non-metamorphosizing larvae was positively correlated with log of concentrations in each of the three insecticides. In contrast, dietary ingestion of acephate had little influence on larval pupation. The rates of non-metamorphosizing larvae were did not significantly difference from that of CK. Moreover, we estimated the expression level of EcR by q-PCR in the insecticide-treated second-instar larvae. Butene-fipronil, fipronil, abamectin at the concentrations equivalent to the corresponding LC50 value significantly increased EcR mRNA level. In contrast, acephate did not enhance the expression of EcR. These results demonstrated that butene-fipronil, fipronil and abamectin are endocrine disrupters, the 3 insecticides caused larvae death by both neurotoxicity and endocrine disrupting. Moreover, our results also revealed that ecdysone-triggering signaling pathway is a potential target. |
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